Anxiety Disorders
Anxiety disorders are a group of psychological problems whose key features include excessive anxiety, fear, worry, avoidance, and compulsive rituals, and produce or result in inordinate morbidity, overutilization of healthcare services, and functional impairment. They are among the most prevalent psychiatric condition in the United States and in most other countries. An incidence of the illness is fairly uniform across cultures. In most cases women are more likely than men to experience anxiety disorders. Chronic anxiety disorders may increase the rate of cardiovascular-related mortality, and hence the proper diagnosis and rapid initiation of treatment must be made.
Anxiety disorders listed in the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition Revised, 1994, published by the American Psychiatric Association, Washington, D.C., U.S.A., pages 393 to 444), include panic disorder with and without agoraphobia, agoraphobia without history of panic disorder, specific phobia, social phobia, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), acute stress disorder, generalized anxiety disorder (GAD), anxiety disorder due to a general medical condition, substance-induced anxiety disorder, specific phobia, and anxiety disorder not otherwise specified.
Panic Disorder With and Without Agoraphobia
Panic disorder is an anxiety disorder whose essential feature is the presence of recurrent panic attacks (i.e. discrete periods of intense fear or discomfort with at least four characteristic associated symptoms). The attacks usually last minutes (or, rarely, hours), are unexpected and do not, as in simple phobia, tend to occur immediately before or on exposure to a situation that almost always causes anxiety. The “unexpected” aspect of the attacks is an essential feature of the disorder. Panic attacks typically begin with the sudden onset of intense apprehension or fear, and are accompanied by physical symptoms such as shortness of breath, dizziness, faintness, choking, palpitations, trembling, sweating, shaking, nausea, numbness, hot flushes or chills, chest pain or the like. Panic disorder may be associated with agoraphobia, in severe cases of which the person concerned is virtually housebound.
Approximately one-third to one-half of individuals diagnosed with panic disorder in community samples also have agoraphobia, although a much higher rate of agoraphobia is encountered in clinical samples.
Agoraphobia Without History of Panic Disorder
Agoraphobia is a condition characterized by the feature of anxiety about being in places or situations from which escape might be difficult (or embarrassing) or in which help may not be available in the event of having a panic attack or panic-like symptoms (e.g., fear of having a sudden attack of dizziness or a sudden attack of diarrhea). Agoraphobia occurs in the context of panic disorder with agoraphobia and agoraphobia without history of panic disorder. The essential features of agoraphobia without history of panic disorder are similar to those of panic disorder with agoraphobia except the focus of fear is on the occurrence of incapacitating or extremely embarrassing panic-like symptoms or limited symptom attacks rather than full panic attacks.
Almost all individuals (over 95%) who present with agoraphobia also have a current diagnosis (or history) or panic disorder. In contrast, the prevalence of agoraphobia without history of panic disorder in epidemiological samples has been reported to be higher than that for panic disorder with agoraphobia.
Obsessive-Compulsive Disorder (OCD)
The primary symptom is recurrent obsessions (i.e., recurrent and intrusive thoughts, images or urges that cause marked anxiety) and/or compulsions (i.e., repetitive behaviors or mental acts that are performed to reduce the anxiety generated by one's obsessions) of sufficient severity to cause distress, be time consuming or to interfere significantly with a person's normal routine or lifestyle. Anxiety is an associated feature of this disorder: an affected person may, for example, show a phobic avoidance of situations that involve the cause of the obsession. Typical obsessions concern contamination, doubting (including self-doubt) and disturbing sexual or religious thoughts. Typical compulsions include washing, checking, ordering things, and counting.
Social Phobia
Social phobia is characterized by the persistent fear of social or performance situations in which embarrassment may occur. Typical situations feared or avoided by individuals with social phoebe include parties, meetings, eating in front of others, writing in front of others, public speaking, conversations, meeting new people, and other related situations. Exposure to social or performance situations almost invariably provokes an immediate anxiety response, as well as sweating, trembling, racing or pounding heart beat, mental confusion, and a desire to flee. Social avoidance and isolation can also become extreme, especially in the more generalized condition. Alcohol abuse is more commonly associated with social phobia than any other anxiety disorder, and frequently represents an attempt at self medication of social fears.
Post-Traumatic Stress Disorder (PTSD)
The principal characteristic symptoms involve re-experiencing a traumatic (i.e. psychologically distressing) event, the avoidance of stimuli associated with that event, the numbing of general responsiveness, and increased arousal. The “events” concerned are outside the range of common experiences such as simple bereavement, chronic illness and marital conflict.
Generalized Anxiety Disorder (GAD)
GAD is a condition of which the essential feature is unrealistic or excessive anxiety, and worry about two or more life circumstances for six months or longer. The worry must be experienced as difficult to control and during that time the affected person is bothered by the concerns for more days than not. When the person is anxious he or she manifests signs of motor tension, autonomic hyperactivity and vigilance and scanning.
Specific Phobia
Specific phobia is an anxiety disorder of which the essential feature is a persistent fear of a circumscribed stimulus, which may be an object or situation, other than fear of having a panic attack or of humiliation or embarrassment in social situations (which falls under social phobia). Examples include phobias of flying, heights, animals, injections, and blood. Simple phobias may be referred to as “specific” phobias and, in the population at large. Exposure to the phobic stimulus will almost invariably lead to an immediate anxiety response.
Multiple causes are suspected for anxiety disorders, especially a combination of genetic makeup, early growth and development, and later life experience. The anxiety disorders are treated with some form of counseling or psychotherapy or pharmacotherapy (drug therapy), either singly or in combination. The medications typically used to treat patients with anxiety disorders are benzodiazepines, selective serotonin reuptake inhibitors (SSRIs), and buspirone.
The benzodiazepines are a large class of relatively safe and widely prescribed medications that have rapid and profound antianxiety and sedative-hypnotic effects. Drugs within the SSRI class are used for the treatment of anxiety disorders such as panic disorder, agoraphobia, OCD, social phobia, post-traumatic stress disorder, specific phobia and broader anxiety disorders [Kaplan & Sadock's Comprehensive textbook of psychiatry 7th. edition, 1, 1441-1498 (1999)]. Buspirone is a relatively selective 5HT1A partial agonist, approved by the FDA as an anxiolytic, most useful for the treatment of GAD, and now frequently used as an adjunct to SSRIs [Kaplan & Sadock's Comprehensive textbook of psychiatry 7th. edition, 1, 1441-1498 (1999)].
There appears to be effective pharmacological and psychological treatments for GAD. Although almost medication studies are based on old criteria for GAD (which have since been substantially revised), there is evidence that a range of pharmacological interventions may be helpful for GAD, including buspirone, imipramine and a variety of benzodiazepines. Pharmacotherapy is considered less effective in GAD than in some other anxiety disorders (Kaplan & Sadock's Comprehensive textbook of psychiatry 7th. edition, 1, 1441-1498 (1999)]. Treatment is usually behavioral exposure. Medications are used occasionally to alleviate the anticipatory anxiety associated with beginning exposure treatment. Low-dose benzodiazepines and β-adrenergic receptor antagonists can be used for this purpose on an as-needed basis.
Concerns have been expressed over possible side effect of some of the medications used to treat anxiety disorders, particularly the benzodiazepines. Common side effects associated with these medications, which may decrease over the course of treatment, include sedation, fatigue, ataxia, slurred speech, and amnesia. Benzodiadepines have also the potential for producing drug dependence (i.e. physiological or behavioral symptoms after discontinuation of use).
There is therefore a continuing need for new agents that are effective and safety anxiolytics.
Adenosine A2A Receptors
Adenosine is known to act via four major receptor subtypes, A1, A2A, A2B, and A3, which have been characterized according to their primary sequences [Pharmacol. Rev., 46, 143-156 (1994)]. Adenosine A2A receptors are abundant in the basal ganglia, especially in the caudate-putamen, nucleus accumbens, and olfactory tubercle in several species [Brain Res., 519, 333-337 (1990)]. The basal ganglia are a critical component of subcortical circuits involved in the integration of sensorimotor, associative, and limbic information to produce motor behavior. In the caudate-putamen, one of the major nuclei in the basal ganglia, adenosine A2A receptors are localized on several neurons and have been shown to modulate the neurotransmission of α-aminobutyric acid (GABA), acetylcholine and glutamate [J. Neurochem., 66, 1882-1888 (1996); J. Neurosci., 16, 605-611 (1996); J. Physiol., 532, 423-434 (2001); Neuroscience, 100; 53-62 (2000); Trends Pharmacol. Sci., 18, 338-344 (1997); and Biosci. Biotechnol. Biochem., 65, 1447-1457 (2001)]. Indeed, adenosine A2A receptor antagonists exhibit significant antiparkinsonian activity [Ann. Neurol., 43, 507-513 (1998); Neurology, 52, 1673-1677 (1999); and Biosci. Biotechnol. Biochem., 65, 1447-1457 (2001)]. Furthermore, current studies suggest linking reward expectation, attention, and cognitions to behavior in the basal ganglia.
More recently, the neuroprotective effect of an adenosine A2A receptor antagonist has been demonstrated in MPTP-induced dopaminergic neurodegeneration [J. Neurochem., 80, 262-270 (2002); and J. Neurosci., 21, RC143 (1-6) (2001)].
Some xanthine compounds are known to show adenosine A2A receptor antagonistic activity, anti-Parkinson's disease activity, antidepressant activity, inhibitory activity on neurodegeneration, or the like (U.S. Pat. Nos. 5,484,920; 5,587,378; and 5,543,415; EP 1016407A1; etc.)
(E)-3-(3-Hydroxypropyl)-1-propyl-8-styrylxanthine is reported to have an anxiolytic activity [Society for Neuroscience Abstracts, (2000). Vol. 26, No. 1-2, pp. Abstract No.-868.17. print. Meeting Info.: 30th Annual Meeting of the Society of Neuroscience New Orleans, La., USA Nov. 4-09, 2000].
Some triazolopyrimidines are reported to have an affinity toward the A2A receptor (WO 02/48145 etc.)
A combination of an adenosine A2A receptor antagonist and an antidepressant or anxiolytic is reported (WO 03/022283). However, there is no data showing the effect of the combination of an adenosine A2A receptor antagonist and an anxiolytic in the above publication.